Put the blackcurrants, sugar and water in a saucepan. Bring to the boil and let it bubble for about 5 minutes. The blackcurrants will break down quickly and the mixture will go quite syrupy.
Press the mixture through a metal sieve and leave to cool.
Stir the yoghurt into the berry mixture. I used an ice cream maker and then poured it into the machine. When the ice cream maker finishes, either eat it immediately or transfer it to another container and put it in the freezer.
If you don't have an ice cream maker, put the mixture into a container in the freezer. Take it out after an hour and whisk it. Return it to the freezer and keep taking it out and whisking it every 20-30 minutes for the next 1.5 hours. It should then be fairly stiff and you can leave it until you are ready to eat it.
Nutritional information is approximate and a guideline only.